Aux port delete for FI discussion
01-30-2010, 07:09 PM
#27
Originally Posted by TeamRX8
argh is a really good user name, it matches exactly what I'm thinking when you're posting this stuff like it's from some hidden secret vault only you know about
01-30-2010, 09:10 PM
#31
still does my head in to think about what is happening here .
If the wastegate has to be closed more to make the same flow how can backpressure be the same ?
I think it more likely that the backpressure is in fact greater but the ratio between pressure at the turbo out let and behind the wastegate is the same ....
If the wastegate has to be closed more to make the same flow how can backpressure be the same ?
I think it more likely that the backpressure is in fact greater but the ratio between pressure at the turbo out let and behind the wastegate is the same ....
01-30-2010, 09:27 PM
#32
Alright so I'm snowed in on a Saturday night (we got hit around here, ice everywhere) and I've got nothing better to do but look up port timing on rotary engines.
So here's a chart with the duration and overlap for series 4 Rx-7 through Series 2 Rx-8, including 4 and 6 port engines:
it was calculated using this: http://www.wallaceracing.com/camcalc.php it's for piston engine cams but that shouldn't matter in this case. The numbers don't seem out of line.
Note how much more aggressive the intake timing is on the Rx-8 6 port motors compared to the earlier peripheral exhaust 6 port engines. Mazda could do that because with the side exhaust ports they didn't have to worry about creating excess overlap which would affect emissions etc.
Also notice how much more aggressive the FD port timing is compared to the equivalent ports on the Rx-8. The secondary ports on an FD 13B-REW are giant compared to everything but a Cosmo engine (2 or 3 rotor). And as you can see that is also a LOT of overlap for a completely stock car, resulting in the exhaust blowback which necessitates a rich idle. The only way they could make that work is because the older rotaries almost always had the air pump leaning out the mixture after it left the exhaust ports.
So here's a chart with the duration and overlap for series 4 Rx-7 through Series 2 Rx-8, including 4 and 6 port engines:
it was calculated using this: http://www.wallaceracing.com/camcalc.php it's for piston engine cams but that shouldn't matter in this case. The numbers don't seem out of line.
Note how much more aggressive the intake timing is on the Rx-8 6 port motors compared to the earlier peripheral exhaust 6 port engines. Mazda could do that because with the side exhaust ports they didn't have to worry about creating excess overlap which would affect emissions etc.
Also notice how much more aggressive the FD port timing is compared to the equivalent ports on the Rx-8. The secondary ports on an FD 13B-REW are giant compared to everything but a Cosmo engine (2 or 3 rotor). And as you can see that is also a LOT of overlap for a completely stock car, resulting in the exhaust blowback which necessitates a rich idle. The only way they could make that work is because the older rotaries almost always had the air pump leaning out the mixture after it left the exhaust ports.
01-30-2010, 10:24 PM
#35
Again, running a 6 port motor with only 4 ports is a little like running a Honda without VTEC. It effectively changes the lift (size of port runner area) and duration (the way the port is cut at the end where it meets the combustion chamber). That affects the powerband at minimum and at some point it may limit total peak power. A lot of the same basic principles of piston engines apply. By closing the aux ports you basically just changed your cam(s).
I did that comparison to answer a few questions I had:
1) how does the port timing of a Renesis 4 port compare to the port timing of a Renesis 6 port with the aux ports closed?
They're pretty close, but the 6 port engine has a little more duration on the primary ports and the exhaust ports. I believe the secondary port casting and runner area is basically the same between the Renesis 4 and 6 port engines, so your "lift" is unchanged.
2) how does the port timing of a Renesis 6 port compare to earlier 6 port engines, which have been turbo'd for many years now?
The Renesis seems better in every respect compared to the older 6 ports, stock-for-stock at least. There's more duration across the board but without any of the inherent drawbacks. That's due to the design of the Rx-8 intake manifolds.
3) how does the port timing and size of a Renesis 6 port engine (running only 4 ports) compare to previous turbo 4 port engines?
IMO not favorably overall, although it's not exactly a direct comparsion. The 6-port-turned-4-port Renesis is probably equal to or maybe even better than the series 4 Rx-7 Turbo engines, which can still do 400whp as long as the turbo is flowing enough.
The FD though has large intake port runners and secondary port timing that's more optimized for this kind of application. It's also got an intake manifold designed for boost and a lot of low/mid range (long runners, small plenum). But again that's not necessarily a fair comparison... because the FD intake ports and intake manifold would not be very good if used in a non turbo application.
Just for the heck of it, here is a comparison between the Cosmo 13B-RE (larger ports than the FD engine) port runners and the series 4 turbo port runners. I've never done a comparison but I suspect the Renesis secondary port runners are a little smaller than the series 4 Rx-7, but I could be wrong.
I guess at these power levels all this is mostly academic, just me indulging my own curiosity.
I did that comparison to answer a few questions I had:
1) how does the port timing of a Renesis 4 port compare to the port timing of a Renesis 6 port with the aux ports closed?
They're pretty close, but the 6 port engine has a little more duration on the primary ports and the exhaust ports. I believe the secondary port casting and runner area is basically the same between the Renesis 4 and 6 port engines, so your "lift" is unchanged.
2) how does the port timing of a Renesis 6 port compare to earlier 6 port engines, which have been turbo'd for many years now?
The Renesis seems better in every respect compared to the older 6 ports, stock-for-stock at least. There's more duration across the board but without any of the inherent drawbacks. That's due to the design of the Rx-8 intake manifolds.
3) how does the port timing and size of a Renesis 6 port engine (running only 4 ports) compare to previous turbo 4 port engines?
IMO not favorably overall, although it's not exactly a direct comparsion. The 6-port-turned-4-port Renesis is probably equal to or maybe even better than the series 4 Rx-7 Turbo engines, which can still do 400whp as long as the turbo is flowing enough.
The FD though has large intake port runners and secondary port timing that's more optimized for this kind of application. It's also got an intake manifold designed for boost and a lot of low/mid range (long runners, small plenum). But again that's not necessarily a fair comparison... because the FD intake ports and intake manifold would not be very good if used in a non turbo application.
Just for the heck of it, here is a comparison between the Cosmo 13B-RE (larger ports than the FD engine) port runners and the series 4 turbo port runners. I've never done a comparison but I suspect the Renesis secondary port runners are a little smaller than the series 4 Rx-7, but I could be wrong.
I guess at these power levels all this is mostly academic, just me indulging my own curiosity.
Last edited by arghx7; 01-30-2010 at 10:34 PM.
01-31-2010, 05:53 AM
#36
Closing off the wastegate will not increase exhaust backpressure-if airflow is the same. Think about it, from the point of WG opening, we are regulating inlet pressure to desired level but overall airflow through the engine increases with RPMs and turbine/WG can pass only so much flow. To drive compressor, we need more energy with increasing RPMs but since we are redirecting quite large part of flow through wastegate, turbine inlet pressure is still climbing to maintain equilibrium.
01-31-2010, 11:56 AM
#38
with aux ports closed :
compressor pressure is higher
compressor/turbine speed is higher
therefore power required to drive turbine is higher
what drives the turbine - air flow at a certain pressure .
Seeing as flow is the same - pressure at the turbine needs to be higher ....
01-31-2010, 12:01 PM
#39
What he is saying is that even with the WG closed; the velocity of the turbine is higher thereby evacuating more exhaust over an equivalent period of time.
So therefore turbo back pressure would be about the same. The theory is sound as long as the turbine doesn't become the restriction to flow.......if it does then the back pressure would be higher.
The other thing that makes me wonder - is other than temperature changes why do this? And here is a fun super secret one... if you gain 2 PSI in dynamic compression but are 5% more efficient what is the total intake heat savings?
0-8 PSI Delta Temp at 80% efficient vs 0-10 PSI Delta Temp at 75% Efficiency.......
So therefore turbo back pressure would be about the same. The theory is sound as long as the turbine doesn't become the restriction to flow.......if it does then the back pressure would be higher.
The other thing that makes me wonder - is other than temperature changes why do this? And here is a fun super secret one... if you gain 2 PSI in dynamic compression but are 5% more efficient what is the total intake heat savings?
0-8 PSI Delta Temp at 80% efficient vs 0-10 PSI Delta Temp at 75% Efficiency.......
01-31-2010, 12:11 PM
#40
The other thing that makes me wonder - is other than temperature changes why do this? And here is a fun super secret one... if you gain 2 PSI in dynamic compression but are 5% more efficient what is the total intake heat savings?
0-8 PSI Delta Temp at 80% efficient vs 0-10 PSI Delta Temp at 75% Efficiency.......
or ----- do you have the formula for calculating delta temp handy Kane ?
Last edited by Brettus; 01-31-2010 at 12:32 PM.
01-31-2010, 12:22 PM
#41
This is a part of the conversation me and Ray had for like 3 days last time he was in HI; it still seems that people can't quite get their head around boost, flow and the like....
The ONLY thing boost pressure matters for is heating of the intake charge....that is IT - a 10:1 compression engine can handle 123444444 PSI of boost with zero latent heat; unfortunately that is physically impossible to do. And the efficiency of the compressor is only the heat savings AFTER intake compression heating - so a 100% efficient compressor is still going to heat the charge.
The ONLY thing boost pressure matters for is heating of the intake charge....that is IT - a 10:1 compression engine can handle 123444444 PSI of boost with zero latent heat; unfortunately that is physically impossible to do. And the efficiency of the compressor is only the heat savings AFTER intake compression heating - so a 100% efficient compressor is still going to heat the charge.
01-31-2010, 12:41 PM
#42
There always seems to be this glimmer of hope - that understanding demonstrates itself in a post or two here and there - but it is always extinguished a few days later.
01-31-2010, 12:58 PM
#43
Just for the heck of it, here is a comparison between the Cosmo 13B-RE (larger ports than the FD engine) port runners and the series 4 turbo port runners. I've never done a comparison but I suspect the Renesis secondary port runners are a little smaller than the series 4 Rx-7, but I could be wrong.
Could be? COULD BE?????
Do you really have any clue to justify posting here? I'm surprised you didn't post this jewel out of your archive of reposted information. Unlike the BS above at least it's relevant, not to mention factual. Be forewarned that the 13B-REW comparison might give you a woodie. I'm only posting it to straighten out your crap:
http://www.rotarydevelopment.net/Rot...790_Rotary.pdf
01-31-2010, 03:13 PM
#44
I'm pretty sure that the majority of those engaged in this discussion probably suffer this affliction.
There always seems to be this glimmer of hope - that understanding demonstrates itself in a post or two here and there - but it is always extinguished a few days later.
There always seems to be this glimmer of hope - that understanding demonstrates itself in a post or two here and there - but it is always extinguished a few days later.
It was you who convinced me this was a good idea in the first place so how about some actual input from you .
What interests me is what is happening outside the displayed efficieny curve . Does efficiency drop more quickly or does it continue to dro off at the same rate ?
01-31-2010, 10:48 PM
#45
Because we keep having the same discussion over and over and over again.
I've already said all there is for me to say on just about every flow-related subject and I've tried to say it in a myriad of different ways to make the kernel understandable to as many people as possible, but I still end up hearing "why don't you say something constructive", so I surrender.
Its all out there.
I've already said all there is for me to say on just about every flow-related subject and I've tried to say it in a myriad of different ways to make the kernel understandable to as many people as possible, but I still end up hearing "why don't you say something constructive", so I surrender.
Its all out there.
01-31-2010, 11:29 PM
#47
02-01-2010, 10:14 AM
#50
I'm getting out of this thread. It's hard to discuss port timing with people who've never ported a motor or at least built one. It's also hard to discuss horsepower and boost with people who've never made much power or run more than 10psi.
